There has been considerable interest in the development of hybrid electronics devices and chips that utilize one or more organic molecules to store information in the discrete oxidation states of the molecule(s) (see, e.g., U.S. Pat. Nos. 6,208,553, 6,212,093, 6,272,038, 6,324,091, 6,381,169, and 6,451,942, and PCT Publication WO 01/03126, etc.).
General challenges in fabricating a hybrid chip containing molecular materials for information storage are that (1) the charge-storage molecule is desirably attached to an electroactive surface, (2) the electrolyte is desirably present in the same location as the charge-storage molecule but not elsewhere, and (3) the counterelectrode is desirably located at a controlled distance from the charge-storage molecules without shorts. Particularly pressing problems are that often the methods for attachment of molecules to surfaces often require very high concentrations, high temperature, and/or the use of reactive intermediates (see, e.g. Cleland et al. (1995) J. Chem. Soc. Faraday Trans. 91: 4001-4003; Buriak (1999) Chem. Commun. 1051-1060; Linford et al. (1995) J. Am. Chem. Soc. 117: 3145-3155; Hamers et al. (2000) Acc. Chem. Res. 33: 617-624; Haber et al. (2000) J. Phys. Chem. B, 104: 9947-9950). Such conditions are readily applicable to small robust molecules but become less satisfactory and often fail altogether as the molecules become larger and/or more elaborate.
One example in this regard is the attachment of molecules to Si or Ge. Thus, the reaction of an alcohol or thiol-containing molecule at elevated temperature (nearly 200° C.) at concentrations≧0.1 M (and often with neat materials; e.g., ˜10 M) affords the siloxane or thiosiloxane linkage (Cleland et al. (1995) J. Chem. Soc. Faraday Trans. 91: 4001-4003). Ferrocene-alcohols tend to attach well under these conditions, porphyrin-alcohols attach less well, and triple-decker lanthanide sandwich coordination compounds bearing an alcohol tend to fail to attach altogether. Charge-storage molecules comprised of multiple triple deckers are ideally suited for storage of multiple bits of information (see, e.g., U.S. Pat. No. 6,212,093 B1; Schweikart et al. (2002) J. Mater. Chem., 12: 808-828), but often cannot be attached to silicon or germanium under these conditions.
A second example employs the reaction of an alkene with a Si surface, affording an alkylsilane linkage (Buriak (1999) Chem. Commun., 1051-1060). This procedure also requires very high concentrations for reaction. A third example is the attachment of charge-storage molecules to glassy carbon. McCreery has described the attachment of diazonium salt derivatives of simple aromatic compounds (e.g., stilbene) to glassy carbon electrodes (Ranganathan et al. (2001) Nanolett., 1: 491-494). However, many redox-active molecules of interest for use in charge-storage applications, particularly those that store charge at low potential, react with diazonium salts. A case in point is given by ferrocene, which undergoes oxidation at 0.22 V versus Ag/Ag+. Aryl diazonium salts are the electrophilic reagents of choice for substitution of the ferrocene nucleus (Weinmayr (1955) J. Am. Chem. Soc., 77: 3012-3014; Broadhead and Pauson (1955) Chem. Soc., 367-370; Gryko et al. (2000) J. Org. Chem. 65: 7356-7362). Thus, ferrocenes, and by extension many other desirable redox-active molecules, cannot be attached or are difficult to attach to glassy carbon via the standard method employing a reactant containing a diazonium salt.
Typically, the surface-attached molecules are either immersed in an electrolyte solution (e.g., Bu4NPF6 in CH2Cl2 solution) or a gel electrolyte (e.g., Bu4NPF6 in propylene carbonate followed by solvent evaporation. While these methods enable studies of the information-storage properties of the molecules, the methods for electrolyte deposition are not very amenable to device fabrication. In particular, it is desirable to be able to locate the electrolyte only in those regions of the chip where the molecules are located, to control the thickness and/or uniformity of the electrolyte layer, and to introduce the counterelectrode without creating shorts across the electrolyte/molecule region. Previously, little control can be exercised over patterning of the electrolyte, which directly affects the methods employed for introducing the counterelectrode.